Actually, converting directly from RF to AF is called Direct Conversion
and that is what Flex radio does. This was also done in the Tentec
Century 21 and 22, and the Heath HW7 and HW8. But the Flex radio scheme
uses a DSP phasing method to remove the audio image so that signals are
only heard on one side of zero beat. The older schemes in the Century
21, 22, HW7, and HW8 had an audio image so that you heard each station
on both sides of zero beat.
Carl Moreschi N4PY
121 Little Bell Dr.
Hays, NC 28635
www.n4py.com
On 4/14/2012 5:19 AM, Rick - DJ0IP / NJ0IP wrote:
> Barbara, this is actually a trick question.
>
> I assume you mean dual "IF" conversion vs. single "IF" conversion.
>
> However now that FlexRadio is on the scene, their definition of single
> conversion is RF straight to AF.
> BTW, this is also the original definition!
>
> For the past 40 years or so, when we said single conversion, we were
> referring to a radio like the original Omni or Argonaut which had a single 9
> MHz IF. We called it single conversion, but actually by definition it is
> dual conversion because the RF is converted to the IF frequency (which is
> actually still RF) and then converted to audio.
>
> Thus dual conversion (as referred to in the past 40 years) and as seen in
> the Omni VI, with 9MHz and 5MHz IF frequencies, was actually triple
> conversion, because the signal still gets converted to audio.
>
> None of this would be worth discussing if Flex had not come out with a new
> version of an old design.
>
>
> So when I read your email, I don't know if you are referring to single
> conversion as used by Flex or single conversion as used by Ten-Tec in the
> Corsair.
>
> If you mean dual-IF-conversion (like Omni VI), there are a couple of
> advantages:
>
> - you need two IF frequencies with small filters (typically crystal) to be
> able to have passband tuning. For instance, the K2 with its single 9MHz IF
> has no passband tuning.
> - good quality filters with maybe 80dB of ultimate attenuation, when used
> in a single conversion rig, will typically have only 60dB of ultimate
> attenuation, due to signal leakage around the filter. If you add a second,
> similar filter with the same IF frequency in series, you get maybe 90 dB,
> but if the second filter is on a different IF frequency, you can get as much
> as 120dB of ultimate attenuation. THESE ARE BALLPARK NUMBERS, but your get
> the idea.
> - dual conversion using a higher "FIRST" IF (above 30 MHz) has the
> advantage that you have fewer birdies which fall inside the ham bands
> (usually none). Radios with single conversion or dual conversion with their
> first conversion on lower frequencies (5MHz or 9MHz) typically have birdies
> which fall within the ham bands... BUT...
> - IF filters at higher frequencies are not nearly of as good of quality as
> those at lower frequencies (due to a thing called fractional bandwidth), so
> you don't have the ultimate attenuation that you have with IF's at lower
> frequencies. This usually deteriorates the close-in DR3 significantly,
> which kills us in contests.
>
> You pays your money and you takes your choice.
> Do you want a good general coverage radio with no birdies in the 0 to 30 MHz
> range, but lesser performance on the ham bands, or do you want a radio with
> much better performance on the ham bands but maybe 2 or 3 birdies (albeit
> usually only S5 or less) within some ham bands?
>
> I WILL GO WITH THE BETTER PERFORMING RIG ANY TIME.
>
> 73
> Rick, DJ0IP
>
> On 08/20/2010 10:37 AM, Barbara wrote:
>> Please tell me some of the improvements dual conversi9on vx. single
> conversion receiver? thanks jjdavis
>
>
>
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>
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